Pluto is fine specimen of a cat. All black, large, fuzzy, and "and sagacious to an astonishing degree" (4). (Sagacious is a cool word to know. It means extremely wise, intelligent, and perceptive.) Over the years Pluto moves from a pampered pet to an abused beast. He is blinded and ultimately murdered by his owner. The narrator might have us believe that he is actually a witch in disguise (see the "Character Analysis" for the narrator's wife more), transforming from witch to Pluto, to the second black cat. To be fair, we gave the second cat his own "Character Analysis," so be sure to check that out. For now, we are focusing on the cat the narrator calls Pluto.
Some critics argue that Pluto is a cat, and only a cat. Others think he's a symbol or allegory for other things. Others think he's both. Since we are all about open reading, we'll go with the third option. Poe had pets of his own, and is suspected to have been an animal lover. At a most basic level, the story seems designed to invite sympathy for animals, and raise awareness of animal abuse. Since you probably don't need a lecture on being nice to cats, we'll focus on a few allegorical and symbolic possibilities.
If it wasn't for the fact that that the cat is black, and that he was hanged from a tree, this interpretation wouldn't work. But, as is shown in several essays in the book Romancing the Shadow: Poe and Race show, it's hard to ignore the possibility that that Pluto is an allegory for a murdered slave. Poe didn't explicitly state his views on race and slavery, so we can't use his views as evidence for the interpretation. Poe's work in general shows a high degree of interest in the pressing legal and social issues of his day. Since Poe was writing before the abolition of slavery in the US, it's likely that slavery was on his mind.
Some readers might be offended by the idea of a black cat representing a black man. As you know, slavery was often justified by the harmful myth that black people were more like animals than human beings. Legally speaking, a slave owner had the same rights over a slave as over an animal. A slave could be bought, sold, abused, or killed, all under the law, just like an animal. Some readers might view Poe's story as perpetuating this harmful idea, or in exploiting fears of slave revolts that were prevalent at the time.
You could also argue that the story tries to show, through the figure of the cat, that both black people, and animals needed protection under the law. Instead of trying to figure out what Poe might have meant if he intended this allegory, we might say that the story expresses anxiety, uncertainly, and fear about the institution of slavery and the treatment of black people in Poe's time. If you want to go deeper, check out Romancing the Shadow, and also Toni Morrison's book Playing in the Dark: Whiteness and the Literary Imagination.
The cat might also be an allegory for a child. Notice that the man and woman don't have any children. This story is concerned with the idea of home and family, and children, like animals, are at the mercy of the adults in charge of them. Poe himself didn't have any kids, that we know of, and children seem mostly absent from his work. In Paragraph 31, the narrator even likens the second black cat's cry to "the sobbing of a child." If this angle interests you, click here for a history of US child protection laws to get you started on a research paper.
Some readers are puzzled by what the man sees on his bedroom wall when he returns to the home after the fire:
I approached and saw, as if graven in bas-relief upon the white surface, the figure of a gigantic cat. […] There was a rope about the animal's neck. (11)
"Bas-relief" is an art term. Click here for some examples and a definition. In "Symbols, Imagery, Allegory" we talk about how the pen-knife the man uses to cut Pluto's eye out, suggests that the story is, on one level, about the process of creating a work of art, and the idea of violence that accompanies this.
According to the narrator, the bas-relief image of the cat, isn't just an image, but the actual body of the cat. So, the dead black cat actually becomes art. This reading suggests that the story expresses anxiety about not just a host of social issues, but about art itself, particularly the finished product.
This isn't the only explanation for this bizarre moment. If you are into science, you might analyze the scientific-sounding explanation the man offers for the phenomenon, and explore the state of science in the 1840s.